The invention is directed to an improved drive coupling and bearing housing for a meat deboning machine and the like.
Experience has shown that bearing life in machines of the type generally shown in U.S. Pat. No. 4,516,731, May 14, 1985, may be quite short. In several instances, the thrust bearing assembly has not lasted an hour. In some cases, the motor bearings last about 1000 hours or less, and rarely do they last a year. The auger support bearing next to the motor usually is changed before it has 300 hours of service. Additionally, the 450.degree. F. drip point grease recommended by the manufacturer drips when the machine is operated according to the instructions.
A review of the assembly reveals that the whole machine is referenced to the C-face of the motor. The auger is supported on the exit end by a motor end coupling attached rigidly to the motor shaft by a bolt and supported by a ball bearing housed in a compression ring support assembly which is bolted to the face of the plate. On the inlet end, the auger is supported by a thrust bearing assembly which in turn is supported by a pair of arms which extend from a plate bolted to the C-face of the motor. This arrangement forms a rigid cage for the rotating elements.
Due to the design, it is not likely for the bearings to have adequate service life because all dimensions relating to bearing linear placement and alignment must be nearly perfect, independent of operating temperature, torque, and thrust, and because the rotating elements are rigidly coupled together with no ability for the auger to float axially, independent of the motor. Further, no provision is made for thermal expansion or internal wear of bearings.
There are critical fits and dimensions in this machine which pertain to alignment and bearing life. The fit between the shaft and shoulder on the inlet end of the auger and the spinner plate or flange auger support is critical. The length between the point of the motor shaft coupling touching the end of the motor shaft and the auger inlet end shoulder touching the spinner plate is critical. This requires that 1) the length between the auger shoulder touching the spinner plate and the auger shoulder touching the shoulder of the motor end shaft coupling be correct, and 2) the dimension from the shoulder of the motor shaft coupling touching the auger shoulder and its point of contact with the end of the motor shaft be correct. The length of the arms supporting the thrust bearing assembly from the front of the plate to the point of contact with the feed can is critical. The thickness of the feed can flange and the depth of the thrust bearing housing from the flange face to its inside end which contacts the thrust bearing support ring are critical. The thickness of the thrust bearing and the thickness of the flange of the spinner plate are critical. The thickness of the mounting plate and the length of the motor shaft from the front of the C-face after it has been cut off by the manufacturer, and the concentricity of the motor coupling bearing housing when fastened are critical. The radial placement of the thrust bearing support arms with respect to the motor C-face, and the concentricity of the thrust bearing housing when fastened are critical.
Depending on how well these critical fits are achieved, different scenarios, each leading to shortened bearing lift, present themselves. In the case where the alignment and fits are good, the auger shoulder transmits thrust to the spinner plate which in turn transmits the thrust to the thrust bearing causing its rollers to turn and to transmit the thrust to the thrust housing which reacts with the support arms and base plate bolted to the C-face of the motor. According to the bearing manufacturer, this bearing is being operated at unsuitably high speeds. As a result the bearing heats up and fails prematurely.
In some instances, users of the machine direct a stream of water on the bearing housing to remove heat, but the bearing still fails prematurely. Following the machine manufacturer's suggestion to add more grease when the temperature rises does not help because this causes the temperature to rise more due to over-lubrication. It has been found that changing the thrust bearing housing to a different design with different bearings has helped achieve longer thrust bearing life, but other bearing problems due to rigid configuration still exist.
When the critical fits, dimensions, and alignment are not perfect, several things can happen depending on how much error exists. If any combination of lengths and thickness allow there to be excessive pressure created on the thrust bearing when the machine is put together for service, the previous scenario repeats itself rapidly. Unfortunately, there is no provision in the machine for floating the auger and pre-loading the thrust bearing so there is no way to control how much pressure is placed on the thrust bearing when the machine is assembled. Additionally, no provision has been made for thermal expansion. In the typical machine, a 150.degree. F. temperature rise can produce a length change of almost 1/16" which is sufficient to produce a great thrust in this configuration. The support arms remain at ambient temperature and do not expand, thus causing this problem.
If any combination of fits, dimensions, and alignment allow the shoulder of the auger not to touch the spinner plate and fail to transmit thrust, the thrust bearing will last longer because the rollers are not turning under load and do not heat up as badly as in the previous scenario. (It is possible that the thrust bearing rollers may not turn at all because there is no method to assure a pre-load.) In U.S. Pat. No. 4,516,731 pin 74 is used to keep the ball bearing 78 and the thrust bearing turning so the spinner plate will not gall to the end of the auger. The thrust causes the motor bearings to wear and allow the motor to be pulled off magnetic center causing the auger to move toward the entry end, thus opening the compression ring which causes yield to drop. Depending on the degree of bearing wear, tightening the compression ring is risky because when the motor is unloaded it floats back to its normal operating point at magnetic center and there may be metal to metal contact with the auger and compression ring when this happens. When the motor is pulled off magnetic center, current increases and leads to motor heating.
Depending on the wear of the motor bearings, fits and dimensions, it may become possible for the load to be transmitted to the thrust bearing at some advanced stage of motor bearing wear, thus causing the thrust bearing to fail before the motor bearings fail completely. This holds the potential for several thrust bearing failures before the motor bearings finally fail. As the motor bearings deteriorate, the axial thrust load is being borne by them, but the radial load is being borne by the auger exit end support bearing. The radial load causes this bearing to fail prematurely.
A major problem with this prior art machine is that the support arms, auger, thrust bearing assembly and feed can are cantilevered and cannot be aligned any better than the back plate and support arms allow. The framework constituting the cage for the rotating elements is not strong enough to prevent deflection under load. Further, the whole cage framework is referenced to the C-face of the motor which is not necessarily perfectly perpendicular to the motor shaft. This means that even if the support arms were able to be perfectly square to the back plate and not defect, that the items supported by them will not necessarily be aligned to the motor shaft.
Keeping the auger in line with the center of the screen and feed can requires that the end of the auger be supported by two self aligning bearings in the idler bearing housing. The problem is that for the auger to be aligned with the center of the feed can and screen, it must be out of alignment with the motor shaft if there is any error in the framework or motor C face orientation. Coupling the auger to the motor shaft eliminates skew and parallel misalignment but does not eliminate angular misalignment.
Accordingly, an important object of the present invention is to provide an improved drive coupling for an auger of a meat deboning machine which eliminates the above described problems.
Another object of the invention is to provide an improved idler bearing assembly for the auger of a meat deboning machine.